An eddy current defect detector utilizing plural rotating search coils in combination with logic circuitry and markers

ABSTRACT

In eddy current defect detecting and marking apparatus, a plurality of search coils are mounted for rotation about an axis coincident with the axis of an elongated article being inspected. A plurality of magnets are mounted for rotation with the search coils and positioned to actuate fixed-position switches. Signals from the search coils and from the switches are utilized in logic circuitry to cause actuation of appropriate ones of a plurality of marking devices depending on where circumferentially and longitudinally of the cylindrical article a detected defect or defects lies for physically marking on the article the defect location.

United States Patent [72] Inventor Joseph Vild [56] References CitedLyndhurst, Ohm UNITED STATES PATENTS g Q J- i g 3,281,667 10/1966Dobbins et al 324/40 i f g; 1971 3,437,918 4/1969 Arnelo 324/37 9Assignee Republic Steel Corporation 3,469,182 9/1969 Wycherley et al.324/37 Cleveland, Ohio Primary Examiner-Rudolph V. Rolinec AssistantExaminer-R. J. Cor'coran Attorneys-Robert P. Wright and Joseph W.Malleck ABSTRACT: In eddy current defect detecting and markingapparatus, a plurality of search coils are mounted for rotation [54]COILS about an axis coincident with the axis of an elongated article INCOMBINATION WITH LOGIC CIRCUITRY AND being inspected. A plurality ofmagnets are mounted for rota- MARKERS tion with the search coils andpositioned to actuate fixed-posi- 43 Cl 6 D tion switches. Signals fromthe search coils and from the p rawmg switches are utilized in logiccircuitry to cause actuation of ap- [52] U.S. Cl. 324/37 propriate onesof a plurality of marking devices depending on [51] Int. Cl G01r 33/12where circumferentially and longitudinally of the cylindrical [50] Fieldof Search 324/34, 37, article a detected defect or defects lies forphysically marking on the article the defect location.

PATENTEDMAR 2|97| 3,568,051

' snmmra INVENTOR JO-SEPH V/LD YQZ AJEQ/ mm /Mmf M ATTOQNEYS.

AN EDDY CURRENT DEFECT DETECTOR UTILIZING lPlLlUlRAL ROTATING SEARCHCOILS IN COMBINATION WITH LOGIC CIRCUITRY AND MARKERS CROSS REFERENCESTO RELATED PATENTS AND APPLICATIONS a. U.S. Pat. No. 2,660,704, issuedNov. 24, 1953 to W. C. Harmon et al. for Seam Depth Indicator;

b. U.S. Pat. No. RE 26,286, re-issued Oct. 17, 1967 to W. C. Harmon forMethod and Apparatus for Inspecting Workpieces which are RelativelyIndependent of Probe Motion";

c. U.S. Pat. application Ser. No. 287,987, filed Jun. 14, 1963 now U.S.Pat. No. 3,418,567 Magnetic Flaw Detector System with Marking FluidApplicator Operable by Variable Pressure of a Control Fluid, andassigned to the assignee of the present invention;

d. U.S. Pat. application Ser. No. 793,652 filed Jan. 24, 1969 by J. M.Mandula et al. for Method and Apparatus for Detecting and MarkingDefects in Articles, and assigned to the assignee of the presentinvention; and

e. U.S. Pat. application Ser. No. 789,204 filed Jan. 6, 1969 by J. Vildet al. for Apparatus for Detecting and Marking Defects in Articles, andassigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION 1 Field of the Invention This inventionrelates to eddy current defect detecting and marking apparatus, and,more particularly, to such apparatus embodying a plurality of searchcoils that rotate about an elongated article, such as a bar or pipe,being inspected.

2. Discussion of the Prior Art The technique of eddy current detectionof flaws in metal articles is well known in the prior art. It involvesmoving a test coil closely over the material being tested. The coil isenergized by an oscillator and generates eddy currents in the steel orother metal being tested. When a flow in the metal is encountered, theloading of the search coil is decreased, and, therefore, the output ofthe oscillator is increased. This variation in oscillator output isdetected and utilized to control signalling or classifying apparatus. Insome types of apparatus, the article being tested may be classifiedaccording to the severity of the defect, while in other types merely thepresence of a defect of greater than a predetermined severity will serveto make the article unusable.

When testing cylindrical articles such as rods or pipes, it hasheretofore been customary to maintain the search coil or probe in afixed position and rotate the cylindrical article about its axis as itmoves axially past the search coil. This has required the provision ofcomplex mechanical equipment for simultaneously rotating the articlebeing tested about its axis while moving it axially past the searchunit. In addition, there remains a possibility that a flaw will beundetected because it does not lie on the helical path traced by thesearch coil.

It has also been customary to mark a detected defect on the materialbeing tested by means of a single marking device. While this results ina mark on the cylindrical article being tested that is very accurate inits longitudinal or axial position, the mark has no relationship to thecircumferential or radial position of the flaw.

Accordingly, it is a general object of the present invention to provideapparatus in which a cylindrical article being tested does not need tobe rotated, and which provides increased accuracy over that heretoforeattainable in detecting and marking the locations of flaws on an articleboth as to longitudinal and circumferential position.

SUMMARY OF THE INVENTION A plurality of search coils are mounted forrotation about an axis coincident with a longitudinal axis of anelongated article being inspected; the article being inspected does notrotate. In the present case, four search coils are utilized, which aremounted 90 apart about the axis of rotation.

An equal number of magnets, corresponding in radial positions to thepositions of the search coils, are mounted for rotation with the searchcoils. The magnets sequentially actuate t:.'o fixed-position switchesmounted 45 apart, as the magnets rotate past the switches.

Signals from the switches are utilized in logic circuitry to identifyfrom which one of eight equal sectors about the circumference of thearticle being inspected a defect signal (if any) originates. In thepresent case, eight fixed-position marking devices are utilized and arerespectively mounted over the centers of the eight sectors. Thus, when amarking device is actuated by a defect signal, it accurately marks theaxial or longitudinal position of a defect and marks the circumferentialposition of the defect within 22%.

BRIEF DESCRIPTION OF THE DRAWINGS in block form in FIG. 4; and

FIG. 6 is a logic diagram similar to FIG. 5, but showing a modified formof logic.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows an elongated article10, such as a bar or pipe, being inspected for defects by means of aneddy current detection technique, The article 10 is moving in adirection from left to right, as seen in the drawing, and passes througha circular rotatable drum mechanism, indicated generally by the numeral12. The cylindrical article 10 is supported and moved axially byconventional conveyor mechanism shown diagrammatically at 14. Themechanism 12 is essentially a circular sleeve or drum supported forrotation in conventional bearings 16 and having a pulley 18 at one end.The pulley 18 may be integral with the circular sleeve or may be securedto it by conventional means. The mechanism 12 is rotated by means of abelt 20 engaging the pulley 18 and conventionally driven by means suchas a motor (not shown).

The mechanism 12 includes two circular bearing rings 22 which areengaged by the bearings 16, and five slip rings 24ae. The slip rings 24are, of course, insulated from each other and from the bearings rings22. The slip rings 24a--e are respectively contacted by brushed 26ae.

Mounted inside the device 12 at radial intervals on the ring 22 are n(in this case, four) search coils 28ad. The search coils 28a-d may be ofthe type disclosed in the referenced U.S. Pat. No. 2,660,704. They arespring mounted by conventional means and ride against the outer surfaceof the article 10 being inspected. One end of the search coil 28a iselectrically connected to the slip ring 24a, and the search coils 2811,c, d, are similarly respectively connected to the slip rings 24b, 0, d.The remaining ends of the search coils 28ad are connected together andto the slip ring 24a. Signals from the n search coils 28 are providedthrough the n slip rings 24 to 11 signal processing channels and tologic circuitry to be later described and, after processing, areutilized to actuate appropriate ones of eight (2n) marking devices 30ahlocated downstream of the rotating drum mechanism 12. The markingdevices 30 are fixed in position, and the signals from the search coils28ad are delayed in time by a sufficient amount to actuate the markingdevices to accurately mark on the article being inspected the axialposition of any defect detected. Which of the marking devices isactuated depends on the search coil from which a defect signaloriginates, as will be later described The mechanical and structuraldetails of the apparatus thus far described and shown in FIG. 1 arefully set forth in the referenced application Ser. No. 793,652, which isincorporated herein by reference.

The marking devices 30 may be of the fluid marking type disclosed in thereferenced application Ser. No. 287,987, or may be of conventionalcommercially available type. They need not be fluid marking devices, butmay be cutting devices for producing nicks or grooves in the articlebeing inspected.

FIG. 2 illustrates in diagrammatic form the relative positions of thesearch coils 28 and the marking devices 30. As shown, the search coils28 are mounted on the rotatable ring 22, which rotates about an axis 32.The axis 32 is coincident with the longitudinal axis of the cylindricalarticle being inspected as shown in FIG. 1. The search coils 28 aremounted x, in this case 90, apart radially about the axis 32. Themarking devices 30 are mounted in fixed position on a supporting ring34. The marking devices 30 are spaced apart radially about the axis 32by x/2, in this case, 45, and are offset substantially 22 A (x/4)radially from the positions of the search coils 28. Thus, as shown, thesearch coils 28 divide the circumference of a cylindrical article beingtested into four quadrants, and the marking devices 30 divide each ofthose quadrants in two 45 sectors. Each marking device 30 is mountedsubstantially in the center of each 45 sector. The radial position ofthe search coil detecting the defect in the article under inspectiondetermines which of the eight marking devices 30 will be actuated tomark the article in the exact or longitudinal position of the defect andwithin 22 of its circumferential or radial position. This isaccomplished by pulse producing means such as magnets and switches, asshown diagrammatically in FIG. 3.

As shown, a plurality of five permanent magnets 36a, b, c, d, e aremounted on a ring 38. The ring 38 is affixed to the drum mechanism 12as, for example, in front of the ring 22 hearing the search coils 28,and rotates with the search coils. The magnet 36a is mounted in the sameradial position as the search coil 28a, and magnets 36b, c, a, arerespectively mounted in the same positions as the search coils 28b, 0,d. A fifth magnet 36e is offset from the magnet 360 by a few degreestoward the magnet 36b.

Mounted on a fixed-position ring 40 are three reed switches 4211, b, c.As shown in FIG. 3, the switch 420 is mounted at approximately 0, whichis angularly the same as the position shown for the magnet 36a, and thesearch coil 28a. The switch 42b is mounted at an angle of 45 withrespect to the switch 42a, and the switch 420 is mounted several degreesin a counterclockwise direction from the switch 420. The magnets 36a, b,c, d and the switches 42a, b are mounted substantially in the sameplane, so that passage of any one of those magnets past either one ofthose switches causes momentary closure of the switch. The magnet 36eand the switch 420 are mounted in a slightly different plane so thatpassage of the magnet 36e affects only the switch 42c and neither of theswitches 42a, 42b, and passage of the magnets 36a, b, c, d does notaffect the switch 42c. The magnet 36e and the switch 42c serve as areset mechanism for the logic circuitry to be later described.

If it is assumed with reference to FIG. 3 that the ring 38 is rotatingin a clockwise direction from the position shown, the switch 420 isfirst actuated by the magnet 36a, then the switch 42b is actuated by themagnet 36a. After 45 more degrees of rotation, the switch 42a isactuated by'the magnet 36d, and then after another 45 rotation theswitch 42b is actuated by that same magnet. This process proceedssequentially with the switch 42a being actuated once for every 90 ofrotation of the ring 38, and the switch 42b being actuated once for each90 of rotation of the ring. The switches 42a, 42b are actuatedalternately at 45 rotational intervals. Once during each rotation of thering 38, the magnet 36e actuates the switch 42c to indicate thecompletion of a rotational cycle and initiate the start of anothercycle. Thus, it is seen that the rotational position of the ring 38 canbe determined within 45 if the number of actuations of the switches 42a,b are counted and the sequence in which they are actuated determined.

FIG. 4 is a block diagram of logic circuitry embodying the invention.Pulse signals are provided to the logic circuitry from the outputs offour signal processing channels 50a, [2, c, d of a signal processor 50.Inputs of the four signal processing channels are respectively connectedto the slip rings 240, b, c, d (FIG. 1) to transmit oscillations to andreceive oscillations from the four search coils 28a, b, c, d. The signalprocessing channels 50 are described and their functions explained indetail in the referenced Pat. application Ser. No. 789,204. Thatapplication is incorporated herein by reference. It is sufficient for aclear understanding of the present application to note that the signalprocessing channels 50 are energized by an oscillator (not shown) at aso-called critical frequency" of the metallic object being inspected.This technique is clearly explained in the referenced U.S. Pat. No. RE26,286.

As explained in the referenced application of Vild et al., when a defectis detected in the material being inspected, the amplitudes of theoscillations coupled to the processing channels 50 from the search coils28 increases. If a flaw is detected by only one of the search coils, theamplitude of the signals provided to its corresponding processingchannel will increase, while the signals provided to the otherprocessing channels will be unaffected in amplitude. Inasmuch as thesignals are transmitted to the processing channels through the sliprings 24 and the brushes 26, it is impossible to tell from the signalitself the radial location of its corresponding search coil when theflaw was detected. It is for this reason that the magnets 36, theswitches 42 and the logic circuitry about to be described are provided.

As shown in FIG. 4, the reed switch 42a is connected between a DC supply(not shown) and an input of a conventional ring counter 52. The reedswitch 420 is connected between the DC supply and a reset input of thering counter 52. As the magnets 36 successively pass the switch 420 andmomentarily cause it to close, the counter 52 is actuated inconventional fashion by the resultant pulses, to provide output signalssuccessively from its four sections 52a, b, c, d. When the magnet 36epasses the switch 420 and causes it to close momentarily, the resultantpulse resets the counter 52 to zero slightly before the next pulse isreceived from the switch 42a. This was explained and is showndiagrammatically in FIG. 3.

Momentary actuation of the switch 420 also provides a pulse signal toone input of a conventional binary counter 54. The counter 54 alsoreceives a pulse signal on a second input each time the switch 42b isactuated. The counter 54 also receives a reset pulse through a diode 55from the reed switch 420 slightly before the next pulse from the switch42a. The binary counter 54 thus receives signals alternately from theswitches 42a, b, at each 45 increment of rotation of the search coils 28and magnets 36, which cause it to change state.

As the switch 42a is successively actuated by the magnets 36a, b, c, d,the ring counter 52 serves to provide output signals successively on itsfour output leads that indicate the positions of the search coils 28with respect to in which of the sectors shown in FIGS. 2 and 3 they arelocated. The binary counter 54, which changes state each time the searchcoils and magnets rotate 45, serves to provide signals that indicatewithin which half or 45 sector of each quadrant the search coils arelocated.

Output signals from the signal processing channels 50 are applied tofour (n) channel selectors 56, 58, 60, 62. Each channel selector 56-62comprises four coincidence gates, which are respectively designated bysuffixes a, b, c, d. Each of the coincidence gates has two inputs, oneof each receives a signal from the signal processor 50 and the other ofwhich receives a signal from the ring counter 52. The input signals toeach gate must bear particular polarity relationships, as will beexplained later, in order to provide an output signal from the gate. Theoutput signals from all four of the gates in each of the channelselectors 56, 58, 60, 62 are combined in each selector to provide oneoutput signal from each selector.

The output of the channel selector 56 is connected to the input of eachof two marker selectors 64a, b. Similarly, the output of the channelselector 58 is connected toan input of each of two marker selectors 64c,d; the output of the channel selector 60 is connected to an input ofmarker selectors 64e, f; and the output of the channel selector 62 isconnected to an input of each of two marker selectors 64g, h. The markerselectors 64 are also coincidence gates. Each has a second input whichis connected to receive a signal from the binary counter 54.Specifically, the second inputs of the marker selectors 64a, c, e, g areconnected to receive a signal of one polarity from the binary counter54, and the marker selectors 64b, d, f, h are connected to receive asignal of opposite polarity. The result is that only one of the markerselectors 64 will provide an output signal at any one time, and theparticular marker selector that is capable of producing an output signalis dependent on the rotational positions (within 45) of the searchcoils.

Output signals from the marker selectors 64a-h are respectively providedas input signals to an equal number of one-shot multivibrators 66a-h.The multivibrators 66 serve to provide time delays to permit a detecteddefect to progress from the axial position of the search coils 28 to theaxial position of the marking devices 30 (FIG. 1). The width of thepulses produced by each multivibrator 66 is, of course, adjustable andis dependent upon the axial speed of travel of the article beinginspected. The output signals of the multivibrators 66bh arerespectively provided to second one-shot or dwell multivibrators 68a-h.The purpose of the multivibrators 68 is to energize the marking devicesfor predetermined lengths of time to make visible marks on the articlebeing inspected. The dwell multivibrators 68 are triggered by thetrailing edges of dwell pulses produced by the one-shot multivibrators66.

OUtput signals of the dwell multivibrators 68 -h are respectivelyprovided to actuate solenoids 70ah. The solenoids 70a-h respectivelycontrol the operation of the markers 30a-h shown in FIG. 1.

The circuitry shown in FIG. 4 is binary in operation. In other words,the amplitudes of the various signals provided to and from the gates areof no particular importance; it is their presence or absence thataffects the operation of the components involved, as is well known inthe computer art. It is pointed out that the signals provided to thechannel selectors 56, 58, 60, 62 from the signal processing channels aresubstantially of equal amplitude, which amplitude bears no relation tothe severity or amplitude of a defect detected by the search coils. Asis shown in the referenced patent application of Vild et al., the outputsignals of the processing channels 50 are provided from one-shotmultivibrators, and hence are of equal amplitudes and durations.

The operation of the circuitry shown in FIG. 4 will be described byusing several specific examples. Assumed conditions in the first exampleare that the search coils 28 and the magnets 36 are in the positionsshown in FIGS. 2 and 3, and that a defect is being detected by thesearch coil 28a. This latter condition means that there is an outputsignal provided from the signal processing channel 501:. For purposes ofexplanation, the presence of a signal is denoted as a 1 condition andthe absence of a signal is denoted as a 0 condition.

In the example chosen, the processing channel 50a is providing a 1output signal as noted, and the other processing channels 50b, c, d, areproviding 0 output signals. Also, the ring counter 52 is providing a 1output signal from its section 52a and 0 output signals from its othersections. The binary counter 54 is providing a 1 output signal on a lead72 and a 0 output signal on a lead 74. Both of the signals from thecounters 52, 54 are caused by momentary actuation of the switch 42a bythe passage of the magnet 36a.

As shown, the channel selector gates 56a, 58a, 60a, 620 are allconnected to receive the output signal from the processing channel 50a.Similarly, all of the b channel selector gates receive input signalsfrom the output of the processing channel 50b; the c channel selectorgates receive input signals from the processing channel 50c; and the dchannel selector gates receive input signals from the processing channel50d. The selector gates 56a, 58d, 60c, and 62b receive signals from thefirst section 52a of the ring counter 52. Similarly, the channelselector gates 56b, 58a, 60a and 620 receive signals from the section52b of the ring counter. The selector gates 56c, 58b, 60a and 62dreceive signals from the section 52c of the counter, and the gates 56d,58c, 60b and 62a receive signals from the counter section 52d. Thus,under the assumed conditions, it is apparent that only the channelselector gate 56a will have two 1 input signals. Therefore, it is theonly selector gate that will provide a 1 output signal. None of theother gates will have coincident 1 input signals, and hence all willprovide 0 output signals. The 1 output signal from the channel selector56 is provided as one input to each of the marker selector gauges 64a,b. The output signals provided by the other channel selectors 58, 60, 62to their respective marker selector gates are all 0.

A second input of each of the four marker selectors 64a, 0, e.g., isconnected to the lead 72 from the binary counter 54. A second input ofeach of the other four marker selectors 64b, 11, f, h is connected tothe lead 74 from the binary counter 54. It will be recalled that theswitch 42a has been closed once to cause the binary counter to provide a1 signal on its lead 72. Therefore is is apparent that the only markerselector 64 that will have two 1 input signals is the selector 64a. Thiswill cause the marker selector 64a to provide an output signal toserially energize the multivibrators 66a, 68a and the solenoid 70a tocause the marker 30a to mark the object being inspected at the center ofthe O45 sector shown in FIG. 2.

If a defect signal had not been detected by the search coil 28 a untilit had rotated clockwise through 45 (FIG. 2), the switch 42b would havebeen actuated by the magnet 360 at the 45 point to reverse the outputsignal conditions of the binary counter 54. In that case, the markerselector 64b would have provided a 1 output signal to energize themultivibrators 66b, 68b and the solenoid 70b. That would actuate themarking device 30b to mark the article being inspected in its 4590sector.

As a further example, consider that a defect is detected by the searchcoil 280 when the coils are in the positions shown in FIG. 2. In thatcase, each of the channel selector gates 56c, 58c, 60c, 620 will receivea 1 input signal from the signal processing channel 500. However, theonly one of those four selector gates that will also receive a 1 inputsignal from the section 52a of the ring counter 52 is the markerselector gate 600. Thus, the marker selector 64e provides a 1 outputsignal to trigger the multivibrators 66e, 68s in series. The solenoid70e will then be energized to actuate the marking device 30e and place amark on the article being inspected which is substantially diametricallyopposed to the position of the mark when the search coil 28a detected adefect.

It is possible to give an example for a defect detected by any of thesearch coils in any of the eight sectors of the cylindrical articlebeing inspected. However, it is believed to be sufficient for a clearunderstanding of the invention if one further and final example isgiven. Therefore, assume that a defect is detected by the search coil28a when it has rotated approximately in a clockwise direction about theobject being inspected from the position shown in FIG. 2. In the case,the magnet 36a will have actuated the switches 420, b, and the magnet36d will have just actuated the switch 42a. This means that the binarycounter 54 will again be providing a 1 output signal on its lead 72 andthe section 52b of the ring counter 52 will be providing a 1 outputsignal.

The 1 output signal from the counter section 52b is provided to thechannel selector gates 56b, 58a, 60d and 62c. Of those four channelselector gates, only the gate 580 will be receiving two 1 input signals.All other channel selector gates will be receiving input signals ofopposite polarities or two signals. It follows then that an outputsignal will be provided only from the channel selector 58. That signalis provided to the marker selectors 640, d. The marker selector 640 isreceiving a 1 input signal on the lead 72 from the binary counter 54,and the selector 64d is receiving a 0 input signal on the lead 74 fromthe counter. Therefore, only the marker selector 64c will provide a 1output signal ro actuate the marker solenoid 700 to mark the articlebeing inspected at the position shown by the marking device 300.

It is pointed out that when the apparatus is first energized, the statesof the binary counter 54 and the ring counter 52 are uncontrolled. Thus,virtually any combinations of search coil position information may bepresent in the system. This information, generally, is incorrect andwould be correct only by coincidence. That combination exists, however,only until the system has been reset during the first revolution of thedrum mechanism 12. When the magnet 36e passes the switch 42c, itactuates that switch to provide a reset voltage pulse to both the ringcounter 52 and binary counter 54. Thus, the system is reset to a 0condition before the magnet 36a actuates the switch 42a to set theoutput of the binary counter 54 to a 1 on its lead 72 and the output ofthe ring counter section 520 to 1.

It is apparent to one skilled in the art that the coincidence gates ofthe channel selectors 56, 58, 60, 62 and the marker selectors 64 maytake many forms, as to their specific logic components and arrangements.For example, the channel selectors 56, 58, 60, 62 may each comprise fourconventional AND gates, the outputs of which are provided to four inputsof an OR gate. The outputs of the four OR gates would then be providedto the marker selectors 64, which may also be conventional AND gates.Such an arrangement was contemplated in the example of various circuitconditions and signals previously given with reference to FIG. 4.

FIG. is a logic diagram of one of the channel selectors 56, 58, 60, 62,specifically the channel selector 56 and the two marker selectorssupplied by the output of that channel selector. It is again pointed outthat the channel selectors 56, 58, 60, 62 are identical in constructionand function, and differ only as to their input and output connections.

As shown in FIG. 5, the channel selector 56 comprises four AND gates7611, b, c, d. The outputs of the AND gates 76 are respectivelyconnected to four inputs of an OR gate 77. The AND gates 76a, b, c, d,respectively, each have one input connected to receive signals from thesignal processing channels 50a, b, c, d. The AND gates 76a, b, c, d,also have second inputs which are respectively connected to receivesignals from the ring counter sections 52a, b, c, d.

The output of the OR gate 77 is connected to one input of each of twoAND gates 78a, b. The AND gates 780, b correspond to the channelselectors 64a, b, shown in FIG. 4. The AND gate 78a has a second input,which is connected to the lead 72 from the binary counter 54 (FIG. 4),and the AND gate 78b has a second input connected to the lead 74 fromthe binary counter 54. The outputs of the AND gates 78a, b, arerespectively connected to the inputs of the multivibrators 66a, bpreviously discussed.

In the first example given with reference to FIG. 4, it was assumed thatthe search coils 28 and the magnets 36 are in the positions shown inFIGS. 2 and 3, and that a defect is being detected by the search coil28a. Under those assumed conditions, the signal processing channel 50ais providing a 1 output signal; the switch 42a has been momentarilyclosed by the magnet 36a to cause a 1 output signal to appear on thelead 72 from the binary counter 54, and to cause a 1 output signal to beprovided from the first section 520 of the ring counter 52.

The signal processing channels 50b, 0, d are all providing 0 outputsignals, as are the ring counter sections 52b, c, d. Similarly, a 0signal appears on the lead 74 from the binary counter 54. Under theseassumed conditions, only the AND gate 76a shown in FIG. 5 receives two 1input signals and produces a 1 output signal, which is supplied to theAND gates 78a, b, through the OR gate 77. The lead 72 is supplying a 1input signal to the AND gate 78a, which in turn provides a 1 outputsignal to actuate the multivibrator 66a. This causes the marking device30a to be actuated to mark the article being inspected in its first 45sector. At that time, the lead 74 is providing a 0 signal to the ANDgate 78b so that AND gate provides a 0 output signal, which does notactuate the multivibrator 66b.

If now the search coils 28 and magnets 36 rotate in a clockwisedirection 45 from their positions shown in FIGS. 2 and 3, the switch 42bwill be momentarily actuated by the magnet 36a to cause the binarycounter 54 to change state. Thus, a 1 signal will be provided on thelead 74, and a 0 signal will be provided on the lead 72. This will causethe AND gate 78a to produce a 0 output signal and the AND gate 78b toproduce a 1 output signal. This causes the multivibrator 66b to beenergized rather than the multivibrator 660, which eventually causes themarking device 30b to be actuated to place a mark on the article beinginspected in the second 45 sector of the article.

FIG. 6 shows a modified form of logic for the channel selectors andmarker selectors. Again, as in the case of FIG. 5, only one channelselector (designated 56) is shown along with its two corresponding twomarker selectors. The logic shown in FIG. 6 differs from that shown inFIG. 5 primarily in that NOR logic elements are used rather than ANDlogic elements. This necessitates a reversal in polarity of the signalsprovided to the channel selectors by the ring counter 52 and the binarycounter 54. In other words, in the example shown in FIG. 4, the lead 72from the binary counter 74 would have a 0 signal thereon and the lead 74would have a 1 signal. In the ring counter 52, the section 52a would beproviding a 0 signal and the sections 52b, 0, d would be providing 1signals. The various sections of the signal processing channels 50 wouldstill provide 1 signals when defects are detected and 0 signals when nodefects are detected. This polarity-reversal practice is well known tothose skilled in the computer art, inasmuch as such counters normallyhave two outputs that provide signals of opposite polarity, and nofurther explanation is believed necessary.

As previously noted, all of the logic elements in the circuitry shown inFIG. 6 are NOR gates. Such a gate is, by definition, one in which allinput signals thereto must be 0 to provide a I output signal, and, ifany one or more of the input signals are ls, the output signal will be0. If all of its inputs are connected together, a NOR gate acts as aninverter and is so used a number of times in the present application.

The principal advantage of such NOR logic circuitry over the ANDcircuitry shown in FIG. 5 is that it is readily available commerciallyin standard packages. For example, such packages are available fromSquare D Company, Milwaukee, Wisconsin and are known as NORPAK solidstate logic controls. Functionally, the circuitry shown in FIG. 6 isidentical to that shown in FIG. 5.

As shown in FIG. 6, signals from the processing channels 50a, b, c, dare respectively provided to the inputs of NOR gates 80a, b, c, d. TheNOR gates 80 are connected as inver ters. The outputs of the NOR gates80a, b, c, d are connected respectively to one input of fourcorresponding NOR gates 82a, b, c, d. Second inputs of the NOR gates82a, b, c, d are respectively connected to receive signals from the ringcounter sections 520, b, c, d. Outputs of the NOR gates 820, b areconnected to inputs of a NOR gate 84a, and outputs of the NOR gates 82c,d are similarly connected to a NOR gate 84b. Output signals of the NORgates 84a, b are respectively inverted by NOR GATES 860, b and providedto two inputs of a l NOR gate 88.

The output of the channel selector 56 is taken from the NOR gate 88 andsupplied as an input to each of two NOR gates 90a, b. The NOR gates 90a,b correspond to the channel selectors 6411, b shown in FIG. 4. A secondinput to the is gate 90a is connected to the lead 72 from the binarycounter 54, and a second input of the NOR gate 90b is connected to thelead 74 from the binary counter. Outputs of the NOR gates 90a, b arerespectively supplied as inputs to the multivibrators 66a, b previouslydescribed.

Assuming that the positions of the search coils 28 and the magnets 36are as shown in FIGS. 2 and 3 and that the search coil 28a is detectinga flaw, a 1 signal will be supplied to the gate 80a and signals will besupplied to the gates 80b, 0, d. These signals are inverted by the gates80 so that a 0 signal is supplied to the NOR gate 820, and 1 signals aresupplied to the NOR gates 82b, 0, d. The second input of the NOR gate82a is supplied with a 0 signal from the ring counter 52a, which causesthat gate to produce a 1 output. The second inputs of the NOR gates 82b,0, d, are supplied with l signals from the ring counter sections 52b, 0,d. The gates 82b, 0, d thus provide 0 output signals.

The 1 and ll signals supplied to the NOR gate 84a cause that gate toproduce a 0 output signal, while the two 0 signals supplied to the NORgate 84b cause that gate to produce a 1 output signal. The signals fromthe gates 84a, b are inverted by the gates 86a, b and provided to thetwo inputs of the NOR gate 88. The l and 0 input signals to the NOR gate88 cause it to produce a 0 output signal.

The 0 output signal provided from the NOR gate 88 is supplied to the twoNOR gates 90a, b. The NOR gate 90a is simultaneously receiving a 0signal on the lead 72 from the binary counter 54, which causes that gateto produce a 1 output signal. This signal is provided to the input ofthe multivibrator 65a to provide a mark on'the article being inspectedin the middle of its first 45 sector.

The NOR gate 90b is receiving a 0 input signal from the gate 88 and a 1input signal on the lead 74 from the binary counter 54. This causes thegate 90b to provide a 0 output signal, which does not trigger itsassociated multivibrator 66b.

If now the search coils 28 and the magnets 36 rotate clockwise 45 fromthe position shown in FIGS. 2 and 3, the switch 42b will be momentarilyclosed. This causes the polarities of the signals on the leads 72, 74from the binary counter 54 to reverse. Thus, the NOR gate 90a willprovide a 0 output signal, whereas the NOR gate 90b will provide a 1output signal. This causes the marking device 30b to be actuated toplace the mark on the article in the second 45 sector.

It is apparent that the same examples used in connection with thedescription referring to FIG. 4 may be applied to the specific logiccircuitry shown in FIGS. 5 and 6. However, this is believed to beunnecessary for a clear understanding of the invention.

It is now seen that the invention achieves the general objective setforth. Apparatus embodying the invention visibly marks defects detectedin a cylindrical article being inspected, with the axial positions ofsuch defects being marked extremely accurately, and with thecircumferential or radial positions of the defects being marked within22% sector of the article. It is also pointed out that the invention isnot limited to the use of any particular number of search coils or anyparticular number of marking devices. If increased circumferentialmarking accuracy is desired, the number of search coils and markingdevices may be increased as necessary to provide the desired accuracy.Of course, the numbers of magnets, switches and channels of logiccircuitry will have to be increased correspondingly.

Although two embodiments of the invention have been shown and described,it is apparent many modifications may be made therein without departingfrom the spirit and scope of the invention.

I claim:

ll. ln eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and havingrotatable search coils where n is any integral number greater than Imounted for rotation about an axis substantially coincident with saidlongitudinal axis and spaced radially about said axes, and having nsignal processing channels respectively connected to said search coilsfor respectively providing defect indicating signals in response to adefect of greater than a predetermined severity being detected by acorresponding search coil, the improvement comprising:

a. of m marking devices fixedly mounted and spaced apart radially aboutsaid axes, m being an integral multiple of n;

b. of n logic channels connected to receive said defect indicatingsignals from said n signal processing channels and in response theretorespectively provide marker actuating signals to said m marking deviceswhen said logic channels are enabled; and

. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidlogic channels as said search coils rotate.

2. In eddy current defect detecting and marking apparatus for inspectingan elongated article having a longitudinal axis and having n rotatablesearch coils where n is any integral number greater than 1 mounted forrotation about an axis substantially coincident with,said longitudinalaxis and equally spaced radially about said axes, and having n signalprocessing channels respectively connected to said search coils forrespectively providing defect indicating signals in response to a defectof greater than a predetermined severity being detected by acorresponding search coil, the improvement comprising:

a. m marking devices fixedly mounted and equally spaced apart radiallyabout said axes, m being an integral multiple of n;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefecting indicating signals occur when said first logic channels areenabled;

m second logic channels connected as n separate groups with m/n secondchannels in each group, to respectively receive said channel selectoroutput signals from said n first logic channels and in response theretorespectively provide marker actuating signals to said m marking deviceswhen said second logic channels are enabled; and

(1. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and succes sively enable said m/n second logicchannels of each said group as said search coils rotate.

3. The improvement of claim I, wherein said position indicating meansincludes:

i. pulse producing means for providing at least one pulse signal eachtime said search coils incrementally rotate through 360/m", and

ii. counting means connected to receive consecutive pulse signals fromsaid pulse producing means and provide said enabling signals tosuccessively enable said logic channels.

4. The improvement of claim 2, wherein said position indicating meansincludes:

i. first pulse producing means for providing a first pulse signal eachtime said search coils incrementally rotate through 360/n;

ii. second pulse producing means for providing a second pulse signaleach time said search coils incrementally rotate through 360lm beyondeach point where said first pulse signal is produced;

iii. first counting means connected to receive consecutive first pulsesignals from said first pulse producing means and successively enablesaid first logic channels as said search coils rotate; and

iv. second counting means connected to receive consecutive first pulsesignals and consecutive second pulse signals from said first and secondpulse producing means and successively enable said m/n second logicchannels of each said group as said search coils rotate.

5. The improvement of claim 4, wherein said first counting 75 means is adigital counter.

6. The improvement of claim 3, wherein said pulse producing meansincludes a plurality of switches fixedly positioned with respect to saidsearch coils, and switch actuating means mounted for rotation with saidsearch coils for actuating said switches.

7. The improvement of claim 6, wherein said switches are reed switches,and said actuating means are magnets.

8. The improvement of claim 1, wherein m equals 2n.

9. The improvement of claim 8, wherein m equals 8 and n equals 4.

10. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than Imounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising:

a. m marking devices fixedly mounted and equally spaced apart radiallyabout said axes, m being an integral multiple of n;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefect indicating signals occur when said first logic channels areenabled;

c. m second logic channels connected as n separate groups with m/nsecond channels in each group, to respectively receive said channelselector output signals from said It first logic channels and inresponse thereto respectively provide marker actuating signals to said mmarking devices when said second logic channels are enabled;

d. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said m/n second logicchannels of each said group as said search coils rotate, said positionindicating means including i. first pulse producing means for providinga first pulse signal each time said search coils incrementally rotatethrough 360/n";

ii. second pulse producing means for providing a second pulse signaleach time said search coils incrementally rotate through 360/m beyondeach point where said first pulse signal is produced;

iii. first counting means connected to receive consecutive first pulsesignals from said first pulse producing means and successively enablesaid first logic channels as said search coils rotate;

iv. second counting means connected to receive consecutive first pulsesignals and consecutive second pulse signals from said first and secondpulse producing means and successively enable said m/n second logicchannels of each said group as said search coils rotate; and

. third pulse producing means for providing a reset pulse to saidcounting means once during each 360 rotation of said search coils.

11. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n any integral number greater than 1mounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising:

a. m marking devices fixedly mounted and equally spaced apart radiallyabout said axes, m being an integral multiple of n;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefect indicating signals occur when said first logic channels areenabled;

c. m second logic channels connected as n separate groups with m/nsecond channels in each group, to respectively receive said channelselector output signals from said n first logic channels and in responsethereto respectively provide marker actuating signals to said In markingdevices when said second logic channels are enabled;

d. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said m/n second logicchannels of each said group as said search coils rotate, said positionindicating means including:

i. pulse producing means for providing at least one pulse signal eachtime said search coils incrementally rotate through 360/n; and

ii. counting means connected to receive consecutive pulse signals fromsaid pulse producing means and provide said enabling signals tosuccessively enable said logic channels.

12. The improvement of claim 4, wherein said first and second pulseproducing means includes a plurality of switches fixedly positioned withrespect to said search coils, and switch actuating means mounted forrotation with said search coils for actuating said switches.

13. The improvement of claim 5, wherein said first and second pulseproducing means includes a plurality of switches fixedly positioned withrespect to said search coils, and switch actuating means mounted forrotation with said search coils for actuating said switches.

14. The improvement of claim 12, wherein said switches are reedswitches, and said actuating means are magnets.

15. The improvement of claim 13, wherein said switches are reedswitches, and said actuating means are magnets.

16. The improvements of claim 5, further including third pulse producingmeans for providing a reset pulse to said counting means once duringeach 360 rotation of said search coils.

17. The improvement of claim 12, further including third pulse producingmeans for providing a reset pulse to said counting means once duringeach 360 rotation of said search coils.

18. The improvement of claim 13, further including third pulse producingmeans for providing a reset pulse to said counting means once duringeach 360 rotation of said search coils.

19. The improvement of claim 16, wherein said switches are reedswitches, and said actuating means are magnets.

20. The improvement of claim 17, wherein said switches are reedswitches, and said actuating means are magnets.

21. ln eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than 1mounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising:

a. m marking devices fixedly mounted and equally spaced apart radiallyabout said axes, m being an integral multiple of n;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefect indicating signals occur when said first logic channels areenabled;

c. m second logic channels connected as n separate groups with m/nsecond channels in each group, to respectively receive said channelselector output signals from said n first logic channels and in responsethereto respectively provide marker actuating signals to said m markingdevices when said second logic channels are enabled;

. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said m/n second logicchannels of each said group as said search coils rotate, said positionindicating means including:

i. first pulse producing means including at least one reed switch and atleast one actuating magnet for providing a first pulse signal each timesaid search coils incrementally rotate through 360/n.

ii. second pulse producing means including at least one reed switch andat least one actuating magnet for providing a second pulse signal eachtime said search coils incrementally rotate through 360/m beyond eachpoint where said first pulse signal is produced,

iii. first counting means comprising a digital counter connected toreceive consecutive first pulse signals from said first pulse producingmeans and successively enable said first logic channels as said searchcoils rotate;

iv. second counting means connected to receive consecutive first pulsesignals and consecutive second pulse signals from said first and secondpulse producing means and successively enable said m/n second logicchannels of each said group as said search coils rotate; and e. thirdpulse producing means for providing a reset pulse to said counting meansonce during each 360 rotation of said search coils.

22. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where m is any integral number greater than Imounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n processing channels respectively connected to said search coilsfor respectively providing defect indicating signals in response to adefect of greater than a predetermined severity being detected by acorresponding search coil, the improvement comprising:

a. 2n marking devices fixedly mounted and equally spaced apart radiallyabout said axes;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefect indicating signals occur when said first logic channels areenabled c. 2n second logic channels connected as n separate groups withtwo second channels in each group, to respectively receive said channelselector output signals from said n first logic channels and in responsethereto respectively provide marker actuating signals to said 2n markingdevices when said second logic channels are enabled; and

d. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said two second logicchannels of each said group as said search coils rotate.

23. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than Imounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising:

a. 2n marking devices fixedly mounted and equally spaced apart radiallyabout said axes;

b. 2n logic channels connected to receive said defect indicating signalsfrom said n signal processing channels and in response theretorespectively provide marker actuating signals to said 2n marking deviceswhen said logic channels are enabled; and

c. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidlogic channels as said search coils rotate, said position indicatingmeans including:

i. pulse producing means for providing at least one pulse signal eachtime said search coils incrementally rotate through l/n; and

ii. counting means connected to receive consecutive pulse signals fromsaid pulse producing means and provide said enabling signals tosuccessively enable said logic channels.

24. in eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than imounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axis, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising:

a. 2n marking devices fixedly mounted and equally spaced apart radiallyabout said axes;

b. n first logic channels all connected to receive said defectindicating signals from said signal processing channels and in responsethereto respectively provide channel selector output signals when saiddefect indicating signals occur when said first logic channels areenabled;

0. n second logic channels connected as n separate groups with twosecond channels in each group, to respectively receive said channelselector output signals from said n first logic channels and in responsethereto respectively provided marker actuating signals to said itmarking devices when said second logic channels are enabled; and

d. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said two second logicchannels of each said group as said search coils rotate; said positionindicating means including:

i. first pulse producing means for providing a first pulse signal eachtime said search coils incrementally rotate through 360/n",

ii. second pulse producing means for providing a second pulse signaleach time said search coils incrementally rotate through l80/n beyondeach point where said first pulse signal is produced;

iii. first counting means connected to receive consecutive first pulsesignals from said first pulse producing means and successively enablesaid first logic channels as said search coils rotate; and

iv. second counting means connected to receive consecutive first pulsesignals and consecutive second pulse signals from said first and secondpulse producing means and successively enable said two second logicchannels of each said group as said search coils rotate.

25. The improvement of claim 6, wherein m equals 2n.

26. The improvement of claim 12, wherein m equals 2n.

27. The improvement of claim 13, wherein m equals 2n.

28. The improvement of claim 14, wherein m equals 2n.

29. The improvement of claim 15, wherein m equals 2n.

30. The improvement of claim 16, wherein m equals 2n.

31. The improvement of claim 17, wherein m equals 2n.

and n equals four.

39. The improvement of claim 13, wherein m equals eight and n equalsfour.

40. The improvement of claim 14, wherein m equals eight and n equalsfour.

41. The improvement of claim 15, wherein m equals eight and n equalsfour.

42. The improvement of claim 16, wherein m equals eight and n equalsfour.

43. The improvement of claim 17, wherein m equals eight and n equalsfour.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 2 568 .O5lDated March 2. 1971 Inventor(s) Joseph Vild It is certified that errorappears in the above-identified pateni and that said Letters Patent arehereby corrected as shown below:

Col. 8 line 73 "is" should be-NOR-.

Col. 9, line 29, after "65a" the following line was omitted: to triggerit and hence to actuate the marking device 30a Col. 9, line 54 "a" wasomitted before 22-1/2.

CLAIMS: Col. 9', line 70 "n" was omitted before "rotatable". Col. 10,line 3 "of" should be deleted.

line 6, "of" should be deleted. Col. 11, line 10, "8" should be-l-. Col.12, line 24 "360/n" should be360/m-/ Col. 13, line 41, "m" should be-n-.Col. 13, line 44 after "n" insert-si'gnal. Col 14 line 27, "axis" shouldbeaxes. Col. 14, line 41, "n" first occurrence should be 2n. Col. 14,line 45, "provided" should be--provide Col. 14 line 45, "n" should be2n.

Signed and sealed this 10th day of August 1971 (SEAL) Attest:

EDWARD M.F'LETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents

1. In eddy current defect detecting and marking apparatus for inspectingan elongated article having a longitudinal axis and having rotatablesearch coils where n is any integral number greater than 1 mounted forrotation about an axis substantially coincident with said longitudinalaxis and spaced radially about said axes, and having n signal processingchannels respectively connected to said search coils for respectivelyproviding defect indicating signals in response to a defect of greaterthan a predetermined severity being detected by a corresponding searchcoil, the improvement comprising: a. of m marking devices fixedlymounted and spaced apart radially about said axes, m being an integralmultiple of n; b. of n logic channels connected to receive said defectindicating signals from said n signal processing channels and inresponse thereto respectively provide marker actuating signals to said mmarking devices when said logic channels are enabled; and c. positionindicating means operatively connected to said rotatable search coilsfor providing enabling signals to successively enable said logicchannels as said search coils rotate.
 2. In eddy current defectdetecting and marking apparatus for inspecting an elongated articlehaving a longitudinal axis and having n rotatable search coils where nis any integral number greater than 1 mounted for rotation about an axissubstantially coincident with said longitudinal axis and equally spacedradially about said axes, and having n signal processing channelsrespectively connected to said search coils for respectively providingdefect indicating signals in response to a defect of greater than apredetermined severity being detected by a corresponding search coil,the improvement comprising: a. m marking devices fixedly mounted andequally spaced apart radially about said axes, m being an integralmultiple of n; b. n first logic channels all connected to receive saiddefect indicating signals from said signal processing channels and inresponse thereto respectively provide channel selector output signalswhen said defecting indicating signals occur when said first logicchannels are enabled; c. m second logic channels connected as n separategroups with m/n second channels in each group, to respectively receivesaid channel selector output signals from said n first logic channelsand in response thereto respectively provide marker actuating signals tosaid m marking devices when said second logic channels are enabled; andd. position indicating means operatively connected to said rotatablesearch coils for providing enabling signals to successively enable saidfirst logic channels and successively enable said m/n second logicchannels of each said group as said search coils rotate.
 3. Theimprovement of claim 1, wherein said position indicating means includes:i. pulse producing means for providing at least one pulse signal eachtime said Search coils incrementally rotate through 360/m*, and ii.counting means connected to receive consecutive pulse signals from saidpulse producing means and provide said enabling signals to successivelyenable said logic channels.
 4. The improvement of claim 2, wherein saidposition indicating means includes: i. first pulse producing means forproviding a first pulse signal each time said search coils incrementallyrotate through 360/n*; ii. second pulse producing means for providing asecond pulse signal each time said search coils incrementally rotatethrough 360/m* beyond each point where said first pulse signal isproduced; iii. first counting means connected to receive consecutivefirst pulse signals from said first pulse producing means andsuccessively enable said first logic channels as said search coilsrotate; and iv. second counting means connected to receive consecutivefirst pulse signals and consecutive second pulse signals from said firstand second pulse producing means and successively enable said m/n secondlogic channels of each said group as said search coils rotate.
 5. Theimprovement of claim 4, wherein said first counting means is a digitalcounter.
 6. The improvement of claim 3, wherein said pulse producingmeans includes a plurality of switches fixedly positioned with respectto said search coils, and switch actuating means mounted for rotationwith said search coils for actuating said switches.
 7. The improvementof claim 6, wherein said switches are reed switches, and said actuatingmeans are magnets.
 8. The improvement of claim 1, wherein m equals 2n.9. The improvement of claim 8, wherein m equals 8 and n equals
 4. 10. Ineddy current defect detecting and marking apparatus for inspecting anelongated article having a longitudinal axis and having n rotatablesearch coils where n is any integral number greater than 1 mounted forrotation about an axis substantially coincident with said longitudinalaxis and equally spaced radially about said axes, and having n signalprocessing channels respectively connected to said search coils forrespectively providing defect indicating signals in response to a defectof greater than a predetermined severity being detected by acorresponding search coil, the improvement comprising: a. m markingdevices fixedly mounted and equally spaced apart radially about saidaxes, m being an integral multiple of n; b. n first logic channels allconnected to receive said defect indicating signals from said signalprocessing channels and in response thereto respectively provide channelselector output signals when said defect indicating signals occur whensaid first logic channels are enabled; c. m second logic channelsconnected as n separate groups with m/n second channels in each group,to respectively receive said channel selector output signals from said nfirst logic channels and in response thereto respectively provide markeractuating signals to said m marking devices when said second logicchannels are enabled; d. position indicating means operatively connectedto said rotatable search coils for providing enabling signals tosuccessively enable said first logic channels and successively enablesaid m/n second logic channels of each said group as said search coilsrotate, said position indicating means including i. first pulseproducing means for providing a first pulse signal each time said searchcoils incrementally rotate through 360/n*; ii. second pulse producingmeans for providing a second pulse signal each time said search coilsincrementally rotate through 360/m* beyond each point where said firstpulse signal is produced; iii. first counting means connected to receiveconsecutive first pulse signals from said first pulse producing meansand successively enable saiD first logic channels as said search coilsrotate; iv. second counting means connected to receive consecutive firstpulse signals and consecutive second pulse signals from said first andsecond pulse producing means and successively enable said m/n secondlogic channels of each said group as said search coils rotate; and e.third pulse producing means for providing a reset pulse to said countingmeans once during each 360* rotation of said search coils.
 11. In eddycurrent defect detecting and marking apparatus for inspecting anelongated article having a longitudinal axis and having n rotatablesearch coils where n any integral number greater than 1 mounted forrotation about an axis substantially coincident with said longitudinalaxis and equally spaced radially about said axes, and having n signalprocessing channels respectively connected to said search coils forrespectively providing defect indicating signals in response to a defectof greater than a predetermined severity being detected by acorresponding search coil, the improvement comprising: a. m markingdevices fixedly mounted and equally spaced apart radially about saidaxes, m being an integral multiple of n; b. n first logic channels allconnected to receive said defect indicating signals from said signalprocessing channels and in response thereto respectively provide channelselector output signals when said defect indicating signals occur whensaid first logic channels are enabled; c. m second logic channelsconnected as n separate groups with m/n second channels in each group,to respectively receive said channel selector output signals from said nfirst logic channels and in response thereto respectively provide markeractuating signals to said m marking devices when said second logicchannels are enabled; d. position indicating means operatively connectedto said rotatable search coils for providing enabling signals tosuccessively enable said first logic channels and successively enablesaid m/n second logic channels of each said group as said search coilsrotate, said position indicating means including: i. pulse producingmeans for providing at least one pulse signal each time said searchcoils incrementally rotate through 360/n*; and ii. counting meansconnected to receive consecutive pulse signals from said pulse producingmeans and provide said enabling signals to successively enable saidlogic channels.
 12. The improvement of claim 4, wherein said first andsecond pulse producing means includes a plurality of switches fixedlypositioned with respect to said search coils, and switch actuating meansmounted for rotation with said search coils for actuating said switches.13. The improvement of claim 5, wherein said first and second pulseproducing means includes a plurality of switches fixedly positioned withrespect to said search coils, and switch actuating means mounted forrotation with said search coils for actuating said switches.
 14. Theimprovement of claim 12, wherein said switches are reed switches, andsaid actuating means are magnets.
 15. The improvement of claim 13,wherein said switches are reed switches, and said actuating means aremagnets.
 16. The improvements of claim 5, further including third pulseproducing means for providing a reset pulse to said counting means onceduring each 360* rotation of said search coils.
 17. The improvement ofclaim 12, further including third pulse producing means for providing areset pulse to said counting means once during each 360* rotation ofsaid search coils.
 18. The improvement of claim 13, further includingthird pulse producing means for providing a reset pulse to said countingmeans once during each 360* rotation of said search coils.
 19. Theimprovement of claim 16, wherein said switches are reed switches, andsaid actuating means are magnEts.
 20. The improvement of claim 17,wherein said switches are reed switches, and said actuating means aremagnets.
 21. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than 1mounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising: a.m marking devices fixedly mounted and equally spaced apart radiallyabout said axes, m being an integral multiple of n; b. n first logicchannels all connected to receive said defect indicating signals fromsaid signal processing channels and in response thereto respectivelyprovide channel selector output signals when said defect indicatingsignals occur when said first logic channels are enabled; c. m secondlogic channels connected as n separate groups with m/n second channelsin each group, to respectively receive said channel selector outputsignals from said n first logic channels and in response theretorespectively provide marker actuating signals to said m marking deviceswhen said second logic channels are enabled; d. position indicatingmeans operatively connected to said rotatable search coils for providingenabling signals to successively enable said first logic channels andsuccessively enable said m/n second logic channels of each said group assaid search coils rotate, said position indicating means including: i.first pulse producing means including at least one reed switch and atleast one actuating magnet for providing a first pulse signal each timesaid search coils incrementally rotate through 360/n*. ii. second pulseproducing means including at least one reed switch and at least oneactuating magnet for providing a second pulse signal each time saidsearch coils incrementally rotate through 360/m* beyond each point wheresaid first pulse signal is produced, iii. first counting meanscomprising a digital counter connected to receive consecutive firstpulse signals from said first pulse producing means and successivelyenable said first logic channels as said search coils rotate; iv. secondcounting means connected to receive consecutive first pulse signals andconsecutive second pulse signals from said first and second pulseproducing means and successively enable said m/n second logic channelsof each said group as said search coils rotate; and e. third pulseproducing means for providing a reset pulse to said counting means onceduring each 360* rotation of said search coils.
 22. In eddy currentdefect detecting and marking apparatus for inspecting an elongatedarticle having a longitudinal axis and having n rotatable search coilswhere m is any integral number greater than 1 mounted for rotation aboutan axis substantially coincident with said longitudinal axis and equallyspaced radially about said axes, and having n processing channelsrespectively connected to said search coils for respectively providingdefect indicating signals in response to a defect of greater than apredetermined severity being detected by a corresponding search coil,the improvement comprising: a. 2n marking devices fixedly mounted andequally spaced apart radially about said axes; b. n first logic channelsall connected to receive said defect indicating signals from said signalprocessing channels and in response thereto respectively provide channelselector output signals when said defect indicating signals occur whensaid first logic channels are enabled c. 2n second logic channelsconnected as n separate groups with two second channels in each group,to respectively receive said channel selector output signals from said nfirst logic channels and in response thereto respectively provide markeractuating signals to said 2n marking devices when said second logicchannels are enabled; and d. position indicating means operativelyconnected to said rotatable search coils for providing enabling signalsto successively enable said first logic channels and successively enablesaid two second logic channels of each said group as said search coilsrotate.
 23. In eddy current defect detecting and marking apparatus forinspecting an elongated article having a longitudinal axis and having nrotatable search coils where n is any integral number greater than 1mounted for rotation about an axis substantially coincident with saidlongitudinal axis and equally spaced radially about said axes, andhaving n signal processing channels respectively connected to saidsearch coils for respectively providing defect indicating signals inresponse to a defect of greater than a predetermined severity beingdetected by a corresponding search coil, the improvement comprising: a.2n marking devices fixedly mounted and equally spaced apart radiallyabout said axes; b. 2n logic channels connected to receive said defectindicating signals from said n signal processing channels and inresponse thereto respectively provide marker actuating signals to said2n marking devices when said logic channels are enabled; and c. positionindicating means operatively connected to said rotatable search coilsfor providing enabling signals to successively enable said logicchannels as said search coils rotate, said position indicating meansincluding: i. pulse producing means for providing at least one pulsesignal each time said search coils incrementally rotate through 180/n*;and ii. counting means connected to receive consecutive pulse signalsfrom said pulse producing means and provide said enabling signals tosuccessively enable said logic channels.
 24. In eddy current defectdetecting and marking apparatus for inspecting an elongated articlehaving a longitudinal axis and having n rotatable search coils where nis any integral number greater than 1 mounted for rotation about an axissubstantially coincident with said longitudinal axis and equally spacedradially about said axis, and having n signal processing channelsrespectively connected to said search coils for respectively providingdefect indicating signals in response to a defect of greater than apredetermined severity being detected by a corresponding search coil,the improvement comprising: a. 2n marking devices fixedly mounted andequally spaced apart radially about said axes; b. n first logic channelsall connected to receive said defect indicating signals from said signalprocessing channels and in response thereto respectively provide channelselector output signals when said defect indicating signals occur whensaid first logic channels are enabled; c. n second logic channelsconnected as n separate groups with two second channels in each group,to respectively receive said channel selector output signals from said nfirst logic channels and in response thereto respectively providedmarker actuating signals to said n marking devices when said secondlogic channels are enabled; and d. position indicating means operativelyconnected to said rotatable search coils for providing enabling signalsto successively enable said first logic channels and successively enablesaid two second logic channels of each said group as said search coilsrotate; said position indicating means including: i. first pulseproducing means for providing a first pulse signal each time said searchcoils incrementally rotate through 360/n*, ii. second pulse producingmeans for providing a second pulse signal each time said search coilsincrementally rotate through 180/n* beyond each point where said firstpulse signal is produced; iii. first counting means connected to receiveconsecutive first pulse signals from said first pulse producing meansand successively enable said first logic channels as said search coilsrotate; and iv. second counting means connected to receive consecutivefirst pulse signals and consecutive second pulse signals from said firstand second pulse producing means and successively enable said two secondlogic channels of each said group as said search coils rotate.
 25. Theimprovement of claim 6, wherein m equals 2n.
 26. The improvement ofclaim 12, wherein m equals 2n.
 27. The improvement of claim 13, whereinm equals 2n.
 28. The improvement of claim 14, wherein m equals 2n. 29.The improvement of claim 15, wherein m equals 2n.
 30. The improvement ofclaim 16, wherein m equals 2n.
 31. The improvement of claim 17, whereinm equals 2n.
 32. The improvement of claim 18, wherein m equals 2n. 33.The improvement of claim 2, wherein m equals eight and n equals four.34. The improvement of claim 3, wherein m equals eight and n equalsfour.
 35. The improvement of claim 4, wherein m equals eight and nequals four.
 36. The improvement of claim 6, wherein m equals eight andn equals four.
 37. The improvement of claim 11, wherein m equals eightand n equals four.
 38. The improvement of claim 12, wherein m equalseight and n equals four.
 39. The improvement of claim 13, wherein mequals eight and n equals four.
 40. The improvement of claim 14, whereinm equals eight and n equals four.
 41. The improvement of claim 15,wherein m equals eight and n equals four.
 42. The improvement of claim16, wherein m equals eight and n equals four.
 43. The improvement ofclaim 17, wherein m equals eight and n equals four.